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Date: Fri, 3 Oct 2014 23:41:24 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Chuck Ebbert <cebbert.lkml@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>, mingo@kernel.org, hpa@zytor.com,
        linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
        peterz@infradead.org, luto@amacapital.net, dvlasenk@redhat.com,
        tglx@linutronix.de
Subject: Re: [tip:x86/asm] x86: Speed up ___preempt_schedule*() by using
	THUNK helpers
Message-ID: <20141003214124.GA31614@redhat.com>
References: <20140921184153.GA23727@redhat.com> <tip-0ad6e3c5199be12c9745da8f8b9e3c9f8066c235@git.kernel.org> <542E2B05.5080607@oracle.com> <20141003083954.10a13a24@as>
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On 10/03, Chuck Ebbert wrote:
>
> > [  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
> > [  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
> > [  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
> > [  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
> > [  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
> > [  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
> > [  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
> > [  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
> > [  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
> > [  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
>
> <snip lots of repeats of this>
>
> I *think* this is because RBP isn't being saved across task switch
> anymore?
>
> Without CONFIG_FRAME_POINTERS that night not be a problem...

Could you please spell?

I don't even understand "RBP isn't being saved", SAVE_CONTEXT/RESTORE_CONTEXT
do push/pop %rbp?

Thanks,

Oleg.